Dolby Digital Surround - It provides an economical and backwards-compatible means for 5.1 soundtracks to carry a sixth, center back surround channel for improved localization of effects. The extra surround channel is matrix encoded onto the discrete left surround and right surround channels of the 5.1 mix, much like the front center channel on Dolby Pro Logic encoded stereo soundtracks. The result can be played without loss of information on standard 5.1 systems, or played in 6.1 or 7.1 on systems with Surround decoding and added speakers. Dolby Digital Surround has since been used for the Star Wars prequels on the DVD versions and also the remastered original Star Wars trilogy. A number of DVDs have a Dolby Digital Surround audio option.
The cinema version of Dolby Digital Surround was introduced in 1999, when Dolby and Skywalker Sound, a division of Lucasfilm Ltd., developed Dolby Digital Surround for the release of Star Wars: Episode I – The Phantom Menace. Dolby Digital Surround has since been used for the Star Wars prequels on the DVD versions and also the remastered original Star Wars trilogy